Phonons of the cis-polyacetylene chain

An investigation of the in-plane phonons of the cis-polyacetylene chain (CH)(x) and isotopic analogs (CD)(x) and ((CH)-C-13)(x) is presented on the basis of a Fourier's dynamical D-matrix formalism. The conjugation is found to be similar to that of the trans-polyacetylene chain. Phonon dispersions have been calculated and follow the shapes predicted by Bozovic. Finally, the most interesting result is that phonon density of states exhibits van Hove singularities whose energies are close to those determined experimentally with incoherent inelastic neutron scattering.